In copending application Ser. No. 622,398, now U.S. Pat. No. 3,462,358, a process is claimed for producing an improved cable oil having an ASTM D-1934 aged dissipation factor (ADF) below 0.010 in the absence of added oxidation inhibitors, from a hydrogenated naphthenic oil having a viscosity in the range of 500-2000 SUS at 100.degree.F., an untraviolet absorbency (UVA) less than 8 at 260 millimicrons and having an ADF greater than 0.015, comprising contacting said oil at a temperature in the range of 100.degree.-400.degree.F., with an adsorbent comprising an acid-activated adsorbent clay in an amount per barrel of oil such that from 10-90 grams of KOH would be required to neutralize the acidity of the acid-activated adsorbent clay. Also claimed is a naphthenic electrical oil having a viscosity in the range of 500-2000 SUS at 100.degree.F., having an ADF less than 0.010 in the absence of added oxidation inhibitors, and which requires at least 75 hours at PFVO test conditions to reach a 6% power factor. It was further disclosed that, in the case of the high viscosity cable oils (4000-6000 SUS at 100.degree.F.), a relatively inexpensive fuller's earth bleaching clay was preferred as the adsorbent for such a hydrorefined oil and that the dosage of clay was not particularly critical insofar as the ADF of the resulting cable oil was concerned.
Also disclosed were hydrogenation conditions and catalysts which could be used to severely hydrorefine distillate oils in the lubricating oil viscosity range (35 and higher SUS at 100.degree.F.). It was further disclosed that such severe hydrogenation should be conducted so that the 260 UVA of the feed to the hydrogenation step be reduced at least 40%.
Further disclosed in said application, by example, was that the degree of nitrogen removal caused by the severe hydrorefining can vary according to the viscosity of the charge oil (an oil having a viscosity of 107 SUS and containing 190 p.p.m. N produced an oil container 47 p.p.m. N; whereas, an oil having a viscosity of 2901 SUS and containing 467 p.p.m. of N produced, under the same hydrogenation conditions, an oil containing 313 p.p.m. of N).